The mounting of discrete electrical components onto printed circuit boards by automated means is well known. For a rather extended period of time, the electrical components, such as resistors, capacitors, inductors, and the like, included axial leads. Over the years, several types of apparatus had been developed to automate this procedure and thereby increase production. Basically, these machines bend the leads, align the components and their leads with respect to lead holes in the printed circuit board to be populated, and then insert the leads into the appropriate holes. The leads are then bent over or clinched to retain the components on the board prior to a soldering operation which both mechanically and electrically bonds the component to the board. In more recent times, however, a new electrical component packaging technique has been developed which does not require through-hole insertion. These are known as surface mounted components or SMC.
Surface mounted components lack or eliminate the long leads associated with through-hole mounted components. SMC's are finding wide use in the electronic industry, and like their leaded counterparts, require accurate placement on printed circuit boards, or other substrate media, prior to soldering. Accordingly, automatic machines have been developed to accomplish this task.
In an early SMC-delivering machine, the components are fed via tubes and apertures and are positioned on a slidable plate, situated over a printed circuit board, in a position which corresponds to the desired position of the components on the board. Subsequently, the plate is displaced while the components are retained so that the components ultimately drop onto the substrate. Due to the uncontrolled dropping motion, there is a risk that the components will tilt, rotate, or land in an incorrect position on the board.
In U.S. Pat. No. 4,393,579, a device for mounting chip-type electronic components on a substrate is disclosed which is designed to enable accurate positioning and mounting of chip-type components such as SMC in a controlled and reproducible manner. This device includes a slide having a recess for accommodating and transporting a component. The component is linearly displaceable in a guide between a loading position and an unloading position, and a suction device which is displaceable in the vertical direction serves to pick up a component from the slide when the latter is in the unloading position, and then move the component downward through a passage in the guide to position the picked-up component onto the substrate positioned underneath the guide. Although this is an improvement over the previously known art, it still leaves much to be desired in speed of operation and reliability.
Also according to the prior art, as exemplified by U.S. Pat. No. 4,381,601, there is disclosed a method for mounting electronic components such as semiconductor pellets or chips to the tip end of an attraction nozzle, holding, and automatically orienting the sucked electronic component by means of a plurality of arms arranged along the outer periphery of the tip end of the sucking nozzle, transferring the held electronic component to a predetermined bonding position on a semiconductor device substrate, and opening the arms to bring down the electronic component onto the predetermined bonding position for bonding. Although this apparatus is adequate for the task of picking up and depositing a component, it does not include a, reliable and accurate means for transporting the component from an input station to a desired location and in exact registration with connection pads on a printed circuit board. In U.S. Pat. Nos. 4,135,630 and 4,290,732 machines are described for picking up electrical components and placing them at desired positions and orientations on a substrate. The pick-up heads of these machines utilize a vacuum or suction tool by which components are held on the head and pawls or fingers are used to position the components on the tools. These devices work well with electrical components of a particular size and shape, but such components are not all similar in dimension. At best these machines can handle a small range of sizes of components. However, it is frequently necessary to position a number of components of widely varying sizes and shapes on a single substrate, and the above-noted prior art devices cannot provide sufficient accuracy and reliability with a single pick-up head without manually adjusting or changing the pawls or fingers, which would be very inconvenient and time-consuming. This problem has been solved in the past by providing a plurality of pick-up heads, each adapted to pick up a different size range of components.
More recently, a head for handling various sizes of electrical components has been described in U.S. Pat. No. 4,624,050. This device includes a head for handling electrical components, the head including a plurality of orienting jaws mounted for movement toward and away from a component carried on a datum face of a tool on a tool holder when the holder is in one of the datum positions. A key feature of this device is that the jaws have a plurality of spaced sets of cooperating datum faces disposed generally transversely to the plane of the datum face of the tool in the holder. Each set of datum faces are disposed so as to be capable of orienting a component carried by a tool mounted on the tool holder when the holder is at a corresponding one of the datum positions. This allows for the handling of a wider variety of component sizes, but still cannot accurately accommodate an infinite variety of component sizes as may be required in the industry.
It should thus be clear that the prior art in the subject area of interest generally lacks the versatility reliability and accuracy required to handle an infinite variety of component sizes of SMC's that is needed in the industry, and that a centering head jaw structure for SMC placement mechanisms which obviates the aforementioned shortcomings would constitute a significant advancement in the art.